Dual-wheeled main landing gears may encounter shimmy vibration under adverse conditions. An analytical investigation is made of energy dissipation from Coulomb friction in oleo main bearings and pressure seal and the contribution to shimmy damping. It is stabilizing but highly variable. Under favorable conditions it exceeds 10 % of critical viscous damping which would rapidly suppress vibration. Under severe conditions, it may be less than 1 %. This may not overcome destabilizing tire dynamics and shimmy incidents are more likely to occur. Strut closure rate and transient disturbances contribute to the loss of damping.